How do you paint plastic with acrylic?

My boyfriend LOVES that new game Guitar Hero... and I want to make his plain plastic guitar into something Amazing. I've got a neat idea for demonic mouth opened wide around the area where you ';strum'; the plastic guitar. I'm wondering how I should go about using acrylics on the plastic. It's slightly textured... but should I rough it up with sand paper and prime it? if so, what should I prime it with?, and should I seal it with something, if so, what? I greatly appreciate any advice you can give me :)How do you paint plastic with acrylic?
Hobby Lobby and Michaels Crafts both carry lines of paints that can be used on specific items (glass, plastic, etc)How do you paint plastic with acrylic?
My sister-in-law loves that game too! As far as painting it goes, the acrylic paint won't adhere to the plastic. You can buy special paint to use on plastics but I think they only come in sprays.(Like to paint outside toys)Try looking at a place like Michaels to see if they have plastic specific paint or have you thought about perm.markers/paint pens? That may be the way to go! Good luck!